Log Message:
Update to 8.20
Add missing DEPENDS

Upstream changes:
forecast 8.20 (2 January 2023)
Improvements to unit tests, and migrate to testthat 3e
Prevent failure in C23 mode
forecast 8.19 (20 November 2022)
Bug fixes
forecast 8.18 (30 September 2022)
Updated RW forecasts to use an unbiased estimate of sigma2
Bug fixes
forecast 8.17 (25 July 2022)
Updated dm.test() to add alternative variance estimators. (#898)
Added simulate.tbats() for simulating from TBATS models.
Added dependency on generics for accuracy() and forecast() (#902)
Bux fixes
forecast 8.16 (10 January 2022)
Fixed tslm() incorrectly applying Box-Cox transformations when an mts is \ 
provided to the data argument (#886).
Set D=0 when auto.arima applied to series with 2m observations or fewer.
Improved performance of parallel search of ARIMA models (jonlachmann, #891).
Fixed scoping of functions used in ggAcf() (#896).
Fixed checks on xreg in simulate.Arima() (#818)
Improved docs and bug fixes.
forecast 8.15 (1 June 2021)
Changed summary() methods to defer console output until print()
Changed default s.window values for mstl(), stlf() and stlm(). The new defaults \ 
are based on extensive empirical testing.
forecast 8.14 (11 March 2021)
Changed default BoxCox(lambda = "auto") lower bound to -0.9.
Use better variance estimates for ets() bias adjustments.
Improved robustness of autoplot.seas() for non-seasonal decomposition.
Fixed scoping of parameters in auto.arima(parallel = TRUE) (#874).
Fixed handling of xreg in tsCV().
forecast 8.13 (11 September 2020)
Fixed forecasts from Arima with drift with initial NAs.
Fixed season colours in gglagplot() to match y-axis (original data).
Fixed facet order for classical decomposition autoplot()
Fixed summary() erroring for tslm() models containing NA values.
forecast 8.12 (21 March 2020)
Fixed bias adjusted forecast mean for ARIMA forecasts.
Improved naming of accuracy() generic formals.
Fix seasonal periods for taylor dataset.
forecast 8.11 (9 February 2020)
The axis for gglagplot() have been reversed for consistency with stats::lag.plot().
forecast 8.10 (4 December 2019)
Updates to remove new CRAN errors
Bug fixes
forecast 8.9 (22 August 2019)
Updates for CRAN policies on Suggests packages
Bug fixes
forecast 8.8 (22 July 2019)
Updates for compatibility with fable
Bug fixes